1. Field of the Invention
The present invention relates to a control system and a control method for a throttle valve driving apparatus. More particularly, the present invention relates to such as to implement an abnormality determination on a sensor for detecting the opening of a throttle valve and a fail-safe operation in the event that such abnormality occurs.
2. Description of the Related Art
JP-A-10-176582 discloses a throttle control system comprising two throttle position sensors for detecting the position of a throttle valve (valve opening) of an internal combustion engine and two accelerator position sensors for detecting the position of an accelerator pedal according to the amount of depression of the accelerator pedal. In the throttle control system, a target opening for the throttle valve is set according to outputs from the accelerator position sensors, and a throttle valve driving motor is controlled such that a valve opening detected by the throttle position sensors becomes the target opening.
In this throttle control system, the abnormality of the throttle position sensors is determined by comparing a deviation between outputs from the two throttle position sensors with a predetermined threshold value. In addition, an abnormality determination is similarly carried out on the accelerator position sensors. Then, in the event that the throttle position sensors are determined abnormal, a fail-safe operation is implemented in which of the two sensor outputs, a sensor outputs which indicates a larger throttle opening is used for control. In addition, in the event that the accelerator position sensors are determined abnormal, a fail-safe operation is implemented in which of two sensor outputs, a sensor output which indicates a smaller-amount of depression of the accelerator pedal is used for control.
As to abnormality that occurs in the throttle control system, there is, for example, a case where it is possible to determine which of the two throttle position sensors is abnormal. In case the aforesaid fail-safe operation is applied in such a case, since the sensor output is selected which attempts to limit further the output of the internal combustion engine, the operability of a vehicle is limited more than required.